Baking soda as a filler only works if the gap is closed at the bottom. Even a microscopic space will let the baking soda fall through. As pointed out, the filler will be very hard when cured, so I carefully wipe off excess baking soda from the surface before applying the glue. And do not let the tip of the nozzle touch the baking soda or it will be instantly clogged. I only use this technique for filling where the issue is structural and not cosmetic.